What Is a “Time-Bandit” Attack in Relation to Double-Spending?

A "time-bandit" attack is an extreme form of a 51% attack where the attacker attempts to rewrite a very long history of the blockchain, potentially reverting thousands of blocks. The attacker aims to steal block rewards and transaction fees from blocks mined long ago, essentially acting as a "time bandit." This is typically only economically viable if the stolen block rewards are immensely valuable and the cost of renting the hashrate for the extended duration is justified.